三效催化剂用CexZr1-xO2固溶体合成技术与储放氧性能研究进展

简要介绍了CexZr1-xO2固溶体的合成方法、微观结构与储放氧性能(OSC)的关系,归纳了从CeO2到CexZr1-xO2固溶体的研究进展过程,提出了今后的工作趋向。     

Properties of thin films of organosilicone compounds for LC alignment

Abstract— Two different methods of fabricating ultrathin films made of organosilicon compounds (OSC) with various chemical structures on both the glass and plastic films has been developed and investigated. There is the adsorption method for linear siloxane derivatives and strained cyclosiloxanes and the Langmuir‐Blodgette method. The physical properties (surface energy with polar and dispersion components and surface charge) of the films were studied as well as their ability to align liquid crystals (LCs). The OSC films have improved stability in ambient environments.     

CexZr1-xO2 储氧材料制备方法研究进展

本文综述了共沉淀法、溶胶-凝胶法、水热法、高能球磨法等常用CexZr1-xO2储氧材料的合成方法,并进行了比较。阐述了CexZr1-xO2的基本改性机制,详述了稀土元素、碱土元素以及过渡金属对CexZr1-xO2的改性效果及原理。相关研究结果表明,CexZr1-xO2晶体结构、形貌、比表面积与其合成方法有很大关系,从而影响其储氧性能和热稳定性。通过掺杂第三种元素与CexZr1-xO2形成三元固溶体能进一步改善其储氧性能和热稳定性,从而使CO和HC在还原条件下以及NOx在氧化条件下的转化率大大提高。最后,本文指出了CexZr1-xO2储氧材料目前存在的问题和今后的研究方向。     

Comparative study of CuO–CeO2 catalysts prepared by wet impregnation and deposition–precipitation

Two different preparation methods are used to synthesize wt. 7% CuO–CeO₂ catalysts: a conventional wet impregnation method, and a deposition–precipitation (DP) method using Na₂CO₃ as precipitating agent. Both samples are characterized by a series of techniques. CuO–CeO₂ (Cu–Ce) prepared by DP shows a lower capacity to release the lattice oxygen to form CO₂. From CO-TPR results, it is demonstrated that this catalyst is not able to reduce copper clusters at low temperatures. Also, CO-TPD shows no CO₂ formation. The activity results confirm the worse performance of Cu–Ce prepared by DP especially when oxygen is not in excess (PROX reaction with stoichometric oxygen). A copper particle size which is too small could create a stronger metal-support interaction, with lower Cu–Ce interface to react.     

650℃一次再热超超临界燃煤发电机组设计优化

针对650℃一次再热超超临界燃煤发电机组热力系统抽汽过热度较高、空气预热器换热温差较大的问题,在650℃基准机组基础上提出加装2级前置式蒸汽冷却器(Outside steam coolers,OSCs)(方案1)和采用前置式空气预热器+OSCs(方案2)进行性能对比研究。通过Ebsilon建模,采用单耗分析法对比了650℃一次再热机组在变工况下的能耗分布情况。结果表明:650℃一次再热机组发电煤耗比600℃二次再热机组降低10.67g·(kW·h)^-1,比700℃一次再热机组高9.77g·(kW·h)^-1(100%THA),节煤效果显著。650℃一次再热不同优化方案中,方案2在各工况下性能均优于方案1和基准机组,方案2发电煤耗246.71g·(kW·h)^-1(100%THA),比方案1降低1.99g·(kW·h)^-1,比基准机组降低3.32g·(kW·h)^-1,在低负荷下仍具有良好的节煤效果。     

一种脉冲振荡电路的分析与设计

采用开关元件控制的恒流充放电是产生稳定非正弦振荡波的主要方法。文章利用施密特(Schmitt)触发器为核心的状态延迟及转换元件，并采用恒流充放电技术，配合精确的时序控制，实现了一种高稳定的低功耗矩形波振荡电路。     

Effects of Pd particle size on the rates of oxygen back-spillover and CO oxidation under dynamic oxygen storage and release measurements over Pd/CeO2 catalysts

A kinetic mathematical model has been applied to investigate for the first time the effects of Pd particle size on the rates of oxygen back-spillover and CO oxidation during Oxygen Storage Capacity (OSC) measurements under dynamic conditions over Pd/CeO₂ catalysts in the 500–700 °C range. The dependence of the intrinsic rate constant k₁ of the CO oxidation reaction on PdO, and that of k ₂ ^app of the oxygen back-spillover from ceria to Pd/PdO on the palladium particle size was estimated by performing curve-fitting of the experimental CO and CO₂ pulse transient responses obtained. Activation energies of 8.0, 9.5 and 21.1 kJ/mol were calculated for the Eley–Rideal step of CO oxidation for the 1.3, 1.8 and 16.4 nm Pd particles, respectively, supported on CeO₂. The transient rates of CO oxidation and oxygen back-spillover were found to decrease with increasing Pd particle size.     

Oxygen storage capacity of La1−xBO3 perovskites (with A′ = Sr, Ce; B = Co, Mn)—relation with catalytic activity in the CH4 oxidation reaction

The aim of this work was to study the effect of cation-substitution on the reducibility of the perovskite, as well as the effect on the catalytic activity for the CH₄ oxidation reaction. Six perovskites (LaCoO₃, LaMnO₃, La_1−xSr_xMnO₃ (x = 0.2, 0.4), and La_1−xCe_xMnO₃ (x = 0.05, 0.1)) were synthesized by reactive grinding. The reducibility of the perovskite was studied by means of the oxygen storage capacity (OSC) measurement. OSC was performed at different temperatures on LaCoO₃ and LaMnO₃, in order to elucidate the different mechanisms of reduction involved at each temperature. The substituted samples showed that reduction profile is modified at high-substitution degrees; however, no differences were observed on the OSC values (amount of most active oxygen, calculated after one pulse of CO) between the pure lanthanum sample and the substituted ones.

Tested in the CH₄ oxidation reaction, the LaCoO₃ sample was found to present a little higher activity than LaMnO₃, even if the cobalt-based sample presented a smaller specific surface area. Moreover, all the substituted samples presented very slightly higher activities than the pure LaMnO₃ solid. Because of the supposed redox oxidation mechanism (Mars-Van-Krevelen), this agrees well with the OSC results obtained for the reducibility of the manganese on these samples, by which it was observed that substitution does not clearly affect the immediate reduction of the manganese.     

Study of the Oxygen Diffusion on Three-Way Catalysts: A Kinetic Model

A computer model was developed to take into account all the phenomena that can occur in ¹⁸O/¹⁶O isotopic exchange over Pt/CeZrO _x materials: adsorption/desorption on the metal, surface and bulk O diffusion. Discriminating each step of the exchange process is no longer necessary: kinetic parameters and O diffusivity can be calculated in a single experiment.     

A Mechanistic Study of Sulfur Poisoning of the Water-Gas-Shift Reaction over Pd/Ceria

The effect of sulfur on the water-gas-shift (WGS) activity of Pd/ceria catalysts has been studied using steady-state rate measurements, pulse-reactor studies, and FTIR. After exposing Pd/ceria to SO₂ at 673 K in an oxidizing environment, the WGS rates dropped to a value close to that observed on Pd/alumina. Both pulse-reactor and FTIR measurements showed that cerium sulfates can be readily reduced by CO and re-oxidized by O₂ at 723 K; however, unlike reduced ceria, the Ce₂O₂S formed by reduction of the sulfates cannot be re-oxidized by H₂O or CO₂. The implications of these measurements for understanding the oxygen-storage capacity (OSC) of three-way catalysts are discussed.